Ultrasonic probes with gas outlets for degassing of molten metals

ABSTRACT

Ultrasonic probes containing a plurality of gas delivery channels are described, as well as ultrasonic probes containing recessed areas near the tip of the probe. These probes can be used in ultrasonic devices, and the ultrasonic devices can be used in molten metal processing operations to reduce the amount of dissolved gasses and impurities in molten metals.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/905,408, filed on Nov. 18, 2013, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

The processing or casting of certain metal articles may require a bathcontaining a molten metal, and this bath of molten metal may bemaintained at a temperature in a range of 700° C. to 1200° C., or more,depending upon the particular metal. Many instruments or devices may beused in the molten metal bath for the production or casting of thedesired metal article. There is a need for these instruments or devicesto better withstand the elevated temperatures encountered in the moltenmetal bath, beneficially having a longer lifetime and limited to noreactivity with the particular molten metal.

Moreover, molten metals may have one or more gasses dissolved in themand/or impurities present in them, and these gasses and/or impuritiesmay negatively impact the final production and casting of the desiredmetal article, and/or the resulting physical properties of the metalarticle itself. Attempts to reduce the amounts of dissolved gasses orimpurities present in molten metal baths have not been completelysuccessful. Accordingly, there is a need for improved devices andmethods to remove gasses and/or impurities from molten metals.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify required oressential features of the claimed subject matter. Nor is this summaryintended to be used to limit the scope of the claimed subject matter.

The present invention is directed to methods for reducing the amount ofa dissolved gas (and/or various impurities) in a molten metal bath(e.g., ultrasonic degassing). In one embodiment, the method may compriseoperating an ultrasonic device in the molten metal bath, and introducinga purging gas into the molten metal bath in close proximity to theultrasonic device. For example, the dissolved gas may comprise hydrogen,the molten metal bath may comprise aluminum or copper (including alloysthereof), and the purging gas may comprise argon and/or nitrogen. Thepurging gas may be added to the molten metal bath within about 50 cm (or25 cm, or 15 cm, or 5 cm, or 2 cm), or through a tip, of the ultrasonicdevice. The purging gas may be added or introduced into the molten metalbath at a rate in a range from about 0.1 to about 150 L/min perultrasonic probe, or additionally or alternatively, at a rate in a rangefrom about 10 to about 500 mL/hr of purging gas per kg/hr of output fromthe molten metal bath.

The present invention also discloses ultrasonic devices, and theseultrasonic devices may be used in many different applications, includingultrasonic degassing and grain refining. As an example, the ultrasonicdevice may comprise an ultrasonic transducer; a probe attached to theultrasonic transducer, the probe comprising a tip; and a gas deliverysystem, the gas delivery system comprising a gas inlet, a gas flow paththrough the probe, and a gas outlet at or near the tip of the probe. Inan embodiment, the probe may be an elongated probe comprising a firstend and a second end, the first end attached to the ultrasonictransducer and the second end comprising a tip. Moreover, the probe maycomprise stainless steel, titanium, niobium, a ceramic, and the like, ora combination of any of these materials. In another embodiment, theultrasonic probe may be a unitary Sialon probe with the integrated gasdelivery system therethrough. In yet another embodiment, the ultrasonicdevice may comprise multiple probe assemblies and/or multiple probes perultrasonic transducer.

In one embodiment of this invention, the ultrasonic probe may comprisetwo or more gas delivery channels extending through the probe andexiting at or near the tip of the probe (e.g., within about 25 cm orabout 20 cm of the tip of the probe; alternatively, within about 15 cm,within about 10 cm, within about 5 cm, within about 2 cm, or withinabout 1 cm, of the tip of the probe; or alternatively, at the tip of theprobe). In another embodiment of this invention, the ultrasonic probemay comprise a gas delivery channel extending through the probe andexiting at or near the tip of the probe, and further, may comprise arecessed region near the tip of the probe.

Both the foregoing summary and the following detailed descriptionprovide examples and are explanatory only. Accordingly, the foregoingsummary and the following detailed description should not be consideredto be restrictive. Further, features or variations may be provided inaddition to those set forth herein. For example, certain embodiments maybe directed to various feature combinations and sub-combinationsdescribed in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this disclosure, illustrate various embodiments of the presentinvention. In the drawings:

FIG. 1A shows a partial cross-sectional view of an ultrasonic probe withmultiple gas channels in an embodiment of the present invention.

FIG. 1B is a perspective view of the ultrasonic probe of FIG. 1A.

FIG. 1C shows a partial cross-sectional view of an ultrasonic deviceusing the ultrasonic probe of FIG. 1A.

FIG. 1D shows a close-up view of the interface between the ultrasonicprobe and the booster of the ultrasonic probe and device of FIGS. 1A-1C.

FIG. 2A shows a partial cross-sectional view of an ultrasonic probe withrecessed regions in an embodiment of the present invention.

FIG. 2B is a perspective view of the ultrasonic probe of FIG. 2A.

FIG. 3 shows a partial cross-sectional view of an ultrasonic device inan embodiment of the present invention.

FIG. 4 shows a partial cross-sectional view of an ultrasonic device inanother embodiment of the present invention.

FIG. 5 shows a partial cross-sectional view of an ultrasonic device inanother embodiment of the present invention.

FIG. 6 shows a partial cross-sectional view of an ultrasonic device inanother embodiment of the present invention.

FIG. 7A shows a partial cross-sectional view of an ultrasonic probe witha single gas channel in an embodiment of the present invention.

FIG. 7B is a perspective view of the ultrasonic probe of FIG. 7A.

FIG. 8 is a plot of hydrogen concentration as a function of time forExamples 1-4.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.Wherever possible, the same or similar reference numbers are used in thedrawings and the following description to refer to the same or similarelements. While embodiments of the invention may be described,modifications, adaptations, and other implementations are possible. Forexample, substitutions, additions, or modifications may be made to theelements illustrated in the drawings, and the methods described hereinmay be modified by substituting, reordering, or adding stages to thedisclosed methods. Accordingly, the following detailed description doesnot limit the scope of the invention.

The terms “a,” “an,” and “the” are intended to include pluralalternatives, e.g., at least one. For instance, the disclosure of “anultrasonic device,” “an elongated probe,” “a purging gas,” etc., ismeant to encompass one, or combinations of more than one, ultrasonicdevice (e.g., one or two or more ultrasonic devices), elongated probe(e.g., one or two or more elongated probes), purging gas (e.g., one ortwo or more purging gasses), etc., unless otherwise specified.

All publications and patents mentioned herein are incorporated herein byreference for the purpose of describing and disclosing, for example, theconstructs and methodologies that are described in the publications,which might be used in connection with the presently describedinvention. The publications discussed throughout the text are providedsolely for their disclosure prior to the filing date of the presentapplication. Nothing herein is to be construed as an admission that theinventors are not entitled to antedate such disclosure by virtue ofprior invention.

Applicant discloses several types of ranges in the present invention.When Applicant discloses or claims a range of any type, Applicant'sintent is to disclose or claim individually each possible number thatsuch a range could reasonably encompass, including end points of therange as well as any sub-ranges and combinations of sub-rangesencompassed therein. For example, in an embodiment of the invention, thepurging gas may be added to the molten metal bath at a rate in a rangefrom about 1 to about 50 L/min per ultrasonic probe. By a disclosurethat the flow rate is in a range from about 1 to about 50 L/min,Applicant intends to recite that the flow rate may be any flow rate inthe range and, for example, may be about 1, about 2, about 3, about 4,about 5, about 6, about 7, about 8, about 9, about 10, about 11, about12, about 13, about 14, about 15, about 16, about 17, about 18, about19, about 20, about 21, about 22, about 23, about 24, about 25, about26, about 27, about 28, about 29, about 30, about 31, about 32, about33, about 34, about 35, about 36, about 37, about 38, about 39, about40, about 41, about 42, about 43, about 44, about 45, about 46, about47, about 48, about 49, or about 50 L/min. Additionally, the flow ratemay be within any range from about 1 to about 50 L/min (for example, therate is in a range from about 2 to about 20 L/min), and this alsoincludes any combination of ranges between about 1 and about 50 L/min.Likewise, all other ranges disclosed herein should be interpreted in asimilar manner.

Embodiments of the present invention may provide systems, methods,and/or devices for the ultrasonic degassing of molten metals. Suchmolten metals may include, but are not limited to, aluminum, copper,steel, zinc, magnesium, and the like, or combinations of these and othermetals (e.g., alloys). Accordingly, the present invention is not limitedto any particular metal or metal alloy. The processing or casting ofarticles from a molten metal may require a bath containing the moltenmetal, and this bath of the molten metal may be maintained at elevatedtemperatures. For instance, molten copper may be maintained attemperatures of around 1100° C., while molten aluminum may be maintainedat temperatures of around 750° C.

As used herein, the terms “bath,” “molten metal bath,” and the like aremeant to encompass any container that might contain a molten metal,inclusive of vessel, crucible, trough, launder, furnace, ladle, and soforth. The bath and molten metal bath terms are used to encompass batch,continuous, semi-continuous, etc., operations and, for instance, wherethe molten metal is generally static (e.g., often associated with acrucible) and where the molten metal is generally in motion (e.g., oftenassociated with a launder).

Many instruments or devices may be used to monitor, to test, or tomodify the conditions of the molten metal in the bath, as well as forthe final production or casting of the desired metal article. There is aneed for these instruments or devices to better withstand the elevatedtemperatures encountered in molten metal baths, beneficially having alonger lifetime and limited to no reactivity with the molten metal,whether the metal is (or the metal comprises) aluminum, or copper, orsteel, or zinc, or magnesium, and so forth.

Furthermore, molten metals may have one or more gasses dissolved inthem, and these gasses may negatively impact the final production andcasting of the desired metal article, and/or the resulting physicalproperties of the metal article itself. For instance, the gas dissolvedin the molten metal may comprise hydrogen, oxygen, nitrogen, sulfurdioxide, and the like, or combinations thereof. In some circumstances,it may be advantageous to remove the gas, or to reduce the amount of thegas in the molten metal. As an example, dissolved hydrogen may bedetrimental in the casting of aluminum (or copper, or other metal oralloy) and, therefore, the properties of finished articles produced fromaluminum (or copper, or other metal or alloy) may be improved byreducing the amount of entrained hydrogen in the molten bath of aluminum(or copper, or other metal or alloy). Dissolved hydrogen over 0.2 ppm,over 0.3 ppm, or over 0.5 ppm, on a mass basis, may have detrimentaleffects on the casting rates and the quality of resulting aluminum (orcopper, or other metal or alloy) rods and other articles. Hydrogen mayenter the molten aluminum (or copper, or other metal or alloy) bath byits presence in the atmosphere above the bath containing the moltenaluminum (or copper, or other metal or alloy), or it may be present inaluminum (or copper, or other metal or alloy) feedstock startingmaterial used in the molten aluminum (or copper, or other metal oralloy) bath.

Attempts to reduce the amounts of dissolved gasses in molten metal bathshave not been completely successful. Often, these processes involveadditional and expensive equipment, as well as potentially hazardousmaterials. For instance, a process used in the metal casting industry toreduce the dissolved gas content of a molten metal may consist of rotorsmade of a material such as graphite, and these rotors may be placedwithin the molten metal bath. Chlorine gas additionally may be added tothe molten metal bath at positions adjacent to the rotors within themolten metal bath. This process will be referred to as the“conventional” process throughout this disclosure, and is often referredto in the industry as rotary gas purging. While the conventional processmay be successful in reducing, for example, the amount of dissolvedhydrogen in a molten metal bath in some situations, this conventionalprocess has noticeable drawbacks, not the least of which are cost,complexity, and the use of potentially hazardous and potentiallyenvironmentally harmful chlorine gas.

Additionally, molten metals may have impurities present in them, andthese impurities may negatively impact the final production and castingof the desired metal article, and/or the resulting physical propertiesof the metal article itself. For instance, the impurity in the moltenmetal may comprise an alkali metal or other metal that is neitherrequired nor desired to be present in the molten metal. As one of skillin the art would recognize, small percentages of certain metals arepresent in various metal alloys, and such metals would not be consideredto be impurities. As non-limiting examples, impurities may compriselithium, sodium, potassium, lead, and the like, or combinations thereof.Various impurities may enter a molten metal bath (aluminum, copper, orother metal or alloy) by their presence in the incoming metal feedstockstarting material used in the molten metal bath. In certain embodimentsof this invention, and unexpectedly, the ultrasonic probes and devices,as well as associated methods, may be capable of reducing an alkalimetal impurity, such as sodium, to less than 1 ppm (by weight) afterultrasonic degassing, from a starting amount of, for example, at leastabout 3 ppm, at least about 4 ppm, from about 3 to about 10 ppm, and thelike.

In addition to undesirable impurities such as alkali metals, moltenmetals also may have inclusions present that may negatively impact thefinal production and casting of the desired metal article, and/or theresulting physical properties of the metal article itself. The totalinclusions or inclusion concentration is typically measured in units ofmm²/kg (mm² of inclusions per kg of metal). In certain embodiments ofthis invention, and unexpectedly, the ultrasonic probes and devices, aswell as associated methods, may be capable of reducing the amount oftotal inclusions by at least about 50%, by comparing the inclusionsbefore and after ultrasonic degassing as described herein. In particularembodiments, the amount of total inclusions may be reduced by at leastabout 60%, at least about 70%, at least about 80%, at least about 90%,at least about 95%, or at least about 98%, and in some cases, up to99-100%.

Embodiments of this invention may provide methods for reducing an amountof a dissolved gas in a molten metal bath or, in alternative language,methods for degassing molten metals. One such method may compriseoperating an ultrasonic device in the molten metal bath, and introducinga purging gas into the molten metal bath in close proximity to theultrasonic device. The dissolved gas may be or may comprise oxygen,hydrogen, sulfur dioxide, and the like, or combinations thereof. Forexample, the dissolved gas may be or may comprise hydrogen. The moltenmetal bath may comprise aluminum, copper, zinc, steel, magnesium, andthe like, or mixtures and/or combinations thereof (e.g., includingvarious alloys of aluminum, copper, zinc, steel, magnesium, etc.). Insome embodiments, the molten metal bath may comprise aluminum, while inother embodiments, the molten metal bath may comprise copper.Accordingly, the molten metal in the bath may be aluminum or,alternatively, the molten metal may be copper.

Moreover, embodiments of this invention may provide methods for reducingan amount of an impurity present in a molten metal bath or, inalternative language, methods for removing impurities. One such methodmay comprise operating an ultrasonic device in the molten metal bath,and introducing a purging gas into the molten metal bath in closeproximity to the ultrasonic device. The impurity may be or may compriselithium, sodium, potassium, lead, and the like, or combinations thereof.For example, the impurity may be or may comprise lithium or,alternatively, sodium. The molten metal bath may comprise aluminum,copper, zinc, steel, magnesium, and the like, or mixtures and/orcombinations thereof (e.g., including various alloys of aluminum,copper, zinc, steel, magnesium, etc.). In some embodiments, the moltenmetal bath may comprise aluminum, while in other embodiments, the moltenmetal bath may comprise copper. Accordingly, the molten metal in thebath may be aluminum or, alternatively, the molten metal may be copper.

The purging gas employed in the methods of degassing and/or methods ofremoving impurities disclosed herein may comprise one or more ofnitrogen, helium, neon, argon, krypton, and/or xenon, but is not limitedthereto. It is contemplated that any suitable gas may be used as apurging gas, provided that the gas does not appreciably react with, ordissolve in, the specific metal(s) in the molten metal bath.Additionally, mixtures or combinations of gases may be employed.According to some embodiments disclosed herein, the purging gas may beor may comprise an inert gas; alternatively, the purging gas may be ormay comprise a noble gas; alternatively, the purging gas may be or maycomprise helium, neon, argon, or combinations thereof; alternatively,the purging gas may be or may comprise helium; alternatively, thepurging gas may be or may comprise neon; or alternatively, the purginggas may be or may comprise argon. Additionally, Applicant contemplatesthat, in some embodiments, the conventional degassing technique may beused in conjunction with ultrasonic degassing processes disclosedherein. Accordingly, the purging gas may further comprise chlorine gasin some embodiments, such as the use of chlorine gas as the purging gasalone or in combination with at least one of nitrogen, helium, neon,argon, krypton, and/or xenon. Moreover, SF₆ can be used singly as apurging gas or in combination with any other purging gas disclosedherein, e.g., nitrogen, argon, etc.

However, in other embodiments of this invention, methods for degassingor for reducing an amount of a dissolved gas in a molten metal bath maybe conducted in the substantial absence of chlorine gas, or with nochlorine gas present. As used herein, a substantial absence means thatno more than 5% chlorine gas by weight may be used, based on the amountof purging gas used. In some embodiments, the methods disclosed hereinmay comprise introducing a purging gas, and this purging gas may beselected from the group consisting of nitrogen, helium, neon, argon,krypton, xenon, and combinations thereof.

The amount of the purging gas introduced into the bath of molten metalmay vary depending on a number of factors. Often, the amount of thepurging gas introduced in a method of degassing molten metals (and/or ina method of removing impurities from molten metals) in accordance withembodiments of this invention may fall within a range from about 0.1 toabout 150 standard liters/min (L/min) for each ultrasonic probe. As oneof skill in the art would readily recognize, more than one ultrasonicprobe can be configured on an ultrasonic device, and more than oneultrasonic device can be utilized in a bath of molten metal (e.g., from1 to 20, from 2 to 20, from 2 to 16, from 4 to 12 devices, etc.). Thus,the purging gas flow rates disclosed herein are intended to describe theflow rates through a single ultrasonic probe. Accordingly, the amount ofthe purging gas introduced may be in a range from about 0.5 to about 100L/min, from about 1 to about 100 L/min, from about 1 to about 50 L/min,from about 1 to about 35 L/min, from about 1 to about 25 L/min, fromabout 1 to about 10 L/min, from about 1.5 to about 20 L/min, from about2 to about 15 L/min, or from about 2 to about 10 L/min, per ultrasonicprobe. These volumetric flow rates are in standard liters per minute,i.e., at a standard temperature (21.1° C.) and pressure (101 kPa). Incircumstances where more than one ultrasonic probe (or more than oneultrasonic device) is used in a bath of molten metal (for instance, 2probes, 3 probes, 4 probes, from 1 to 8 probes, from 2 to 8 probes, from1 to 4 probes, and so forth, per device), the purging gas flow rate foreach probe, independently, may be in a range from about 0.1 to about 50L/min, from about 0.5 to about 30 L/min, from about 1 to about 30 L/min,from about 2 to about 50 L/min, from about 2 to about 25 L/min, fromabout 3 to about 50 L/min, or from about 4 to about 25 L/min.

In continuous or semi-continuous molten metal operations, the amount ofthe purging gas introduced into the bath of molten metal may vary basedon the molten metal output or production rate. Accordingly, the amountof the purging gas introduced in a method of degassing molten metals(and/or in a method of removing impurities from molten metals) inaccordance with such embodiments may fall within a range from about 10to about 500 mL/hr of purging gas per kg/hr of molten metal (mL purginggas/kg molten metal). In some embodiments, the ratio of the volumetricflow rate of the purging gas to the output rate of the molten metal maybe in a range from about 10 to about 400 mL/kg; alternatively, fromabout 15 to about 300 mL/kg; alternatively, from about 20 to about 250mL/kg; alternatively, from about 30 to about 200 mL/kg; alternatively,from about 40 to about 150 mL/kg; or alternatively, from about 50 toabout 125 mL/kg. As above, the volumetric flow rate of the purging gasis at a standard temperature (21.1° C.) and pressure (101 kPa).

Methods for degassing molten metals consistent with embodiments of thisinvention may be effective in removing greater than about 10 weightpercent of the dissolved gas present in the molten metal bath, i.e., theamount of dissolved gas in the molten metal bath may be reduced bygreater than about 10 weight percent from the amount of dissolved gaspresent before the degassing process was employed. In some embodiments,the amount of dissolved gas present may be reduced by greater than about15 weight percent, greater than about 20 weight percent, greater thanabout 25 weight percent, greater than about 35 weight percent, greaterthan about 50 weight percent, greater than about 75 weight percent, orgreater than about 80 weight percent, from the amount of dissolved gaspresent before the degassing method was employed. For instance, if thedissolved gas is hydrogen, levels of hydrogen in a molten bathcontaining aluminum or copper greater than about 0.3 ppm or 0.4 ppm or0.5 ppm (on a mass basis) may be detrimental and, often, the hydrogencontent in the molten metal may be about 0.4 ppm, about 0.5 ppm, about0.6 ppm, about 0.7 ppm, about 0.8 ppm, about 0.9 ppm, about 1 ppm, about1.5 ppm, about 2 ppm, or greater than 2 ppm. It is contemplated thatemploying the methods disclosed in embodiments of this invention mayreduce the amount of the dissolved gas in the molten metal bath to lessthan about 0.4 ppm; alternatively, to less than about 0.3 ppm;alternatively, to less than about 0.2 ppm; alternatively, to within arange from about 0.1 to about 0.4 ppm; alternatively, to within a rangefrom about 0.1 to about 0.3 ppm; or alternatively, to within a rangefrom about 0.2 to about 0.3 ppm. In these and other embodiments, thedissolved gas may be or may comprise hydrogen, and the molten metal bathmay be or may comprise aluminum and/or copper.

Embodiments of this invention directed to methods of degassing (e.g.,reducing the amount of a dissolved gas in bath comprising a moltenmetal) or to methods of removing impurities may comprise operating anultrasonic device in the molten metal bath. The ultrasonic device maycomprise an ultrasonic transducer and an elongated probe, and the probemay comprise a first end and a second end. The first end may be attachedto the ultrasonic transducer and the second end may comprise a tip, andthe tip of the elongated probe may comprise niobium. Specifics onillustrative and non-limiting examples of ultrasonic devices that may beemployed in the processes and methods disclosed herein will be discussedfurther below. As it pertains to an ultrasonic degassing process or to aprocess for removing impurities, the purging gas may be introduced intothe molten metal bath, for instance, at a location near the ultrasonicdevice. Often, the purging gas may be introduced into the molten metalbath at a location near the tip of the ultrasonic device. It iscontemplated that the purging gas may be introduced into the moltenmetal bath within about 1 meter of the tip of the ultrasonic device,such as, for example, within about 100 cm, within about 50 cm, withinabout 40 cm, within about 30 cm, within about 25 cm, or within about 20cm, of the tip of the ultrasonic device. In some embodiments, thepurging gas may be introduced into the molten metal bath within about 15cm of the tip of the ultrasonic device; alternatively, within about 10cm; alternatively, within about 8 cm; alternatively, within about 5 cm;alternatively, within about 3 cm; alternatively, within about 2 cm; oralternatively, within about 1 cm. In a particular embodiment, thepurging gas may be introduced into the molten metal bath adjacent to orthrough the tip of the ultrasonic device.

While not intending to be bound by this theory, Applicant believes thata synergistic effect may exist between the use of an ultrasonic deviceand the incorporation of a purging gas in close proximity, resulting ina dramatic reduction in the amount of a dissolved gas in a bathcontaining molten metal. Applicant believes that the ultrasonic energyproduced by the ultrasonic device may create cavitation bubbles in themelt, into which the dissolved gas may diffuse. However, Applicantbelieves that, in the absence of the purging gas, many of the cavitationbubbles may collapse prior to reaching the surface of the bath of moltenmetal. Applicant believes that the purging gas may lessen the amount ofcavitation bubbles that collapse before reaching the surface, and/or mayincrease the size of the bubbles containing the dissolved gas, and/ormay increase the number of bubbles in the molten metal bath, and/or mayincrease the rate of transport of bubbles containing dissolved gas tothe surface of the molten metal bath. Regardless of the actualmechanism, Applicant believes that the use of an ultrasonic device incombination with a source of a purging gas in close proximity mayprovide a synergistic improvement in the removal of the dissolved gasfrom the molten metal bath, and a synergistic reduction in the amount ofdissolved gas in the molten metal. Again, while not wishing to be boundby theory, Applicant believes that the ultrasonic device may createcavitation bubbles within close proximity to the tip of the ultrasonicdevice. For instance, for an ultrasonic device having a tip with adiameter of about 2 to 5 cm, the cavitation bubbles may be within about15 cm, about 10 cm, about 5 cm, about 2 cm, or about 1 cm of the tip ofthe ultrasonic device before collapsing. If the purging gas is added ata distance that is too far from the tip of the ultrasonic device, thepurging gas may not be able to diffuse into the cavitation bubbles.Hence, while not being bound by theory, Applicant believes that it maybe beneficial for the purging gas to be introduced into the molten metalbath near the tip of the ultrasonic device, for instance, within about25 cm or about 20 cm of the tip of the ultrasonic device, and morebeneficially, within about 15 cm, within about 10 cm, within about 5 cm,within about 2 cm, or within about 1 cm, of the tip of the ultrasonicdevice.

Ultrasonic devices in accordance with embodiments of this invention maybe in contact with molten metals such as aluminum or copper, forexample, as disclosed in U.S. Patent Publication No. 2009/0224443, whichis incorporated herein by reference in its entirety. In an ultrasonicdevice for reducing dissolved gas content (e.g., hydrogen) in a moltenmetal, niobium or an alloy thereof may be used as a protective barrierfor the device when it is exposed to the molten metal, or as a componentof the device with direct exposure to the molten metal.

Embodiments of the present invention may provide systems and methods forincreasing the life of components directly in contact with moltenmetals. For example, embodiments of the invention may use niobium toreduce degradation of materials in contact with molten metals, resultingin significant quality improvements in end products. In other words,embodiments of the invention may increase the life of or preservematerials or components in contact with molten metals by using niobiumas a protective barrier. Niobium may have properties, for example itshigh melting point, which may help provide the aforementionedembodiments of the invention. In addition, niobium also may form aprotective oxide barrier when exposed to temperatures of about 200° C.and above.

Moreover, embodiments of the invention may provide systems and methodsfor increasing the life of components directly in contact or interfacingwith molten metals. Because niobium has low reactivity with certainmolten metals, using niobium may prevent a substrate material fromdegrading. Consequently, embodiments of the invention may use niobium toreduce degradation of substrate materials resulting in significantquality improvements in end products. Accordingly, niobium inassociation with molten metals may combine niobium's high melting pointand its low reactivity with molten metals, such as aluminum and/orcopper.

In some embodiments, niobium or an alloy thereof may be used in anultrasonic device comprising an ultrasonic transducer and an elongatedprobe. The elongated probe may comprise a first end and a second end,wherein the first end may be attached to the ultrasonic transducer andthe second end may comprise a tip. In accordance with this embodiment,the tip of the elongated probe may comprise niobium (e.g., niobium or analloy thereof). The ultrasonic device may be used in an ultrasonicdegassing process, as discussed above. The ultrasonic transducer maygenerate ultrasonic waves, and the probe attached to the transducer maytransmit the ultrasonic waves into a bath comprising a molten metal,such as aluminum, copper, zinc, steel, magnesium, and the like, ormixtures and/or combinations thereof (e.g., including various alloys ofaluminum, copper, zinc, steel, magnesium, etc.).

Referring first to FIG. 3, which illustrates using niobium and othermaterials in an ultrasonic device 300, which may be used to reducedissolved gas content in a molten metal. The ultrasonic device 300 mayinclude an ultrasonic transducer 360, a booster 350 for increasedoutput, and an ultrasonic probe assembly 302 attached to the transducer360. The ultrasonic probe assembly 302 may comprise an elongatedultrasonic probe 304 and an ultrasonic medium 312. The ultrasonic device300 and ultrasonic probe 304 may be generally cylindrical in shape, butthis is not a requirement. The ultrasonic probe 304 may comprise a firstend and a second end, wherein the first end comprises an ultrasonicprobe shaft 306 which is attached to the ultrasonic transducer 360. Theultrasonic probe 304 and the ultrasonic probe shaft 306 may beconstructed of various materials. Exemplary materials may include, butare not limited to, stainless steel, titanium, niobium, a ceramic (e.g.,a Sialon, a Silicon carbide, a Boron carbide, a Boron nitride, a Siliconnitride, an Aluminum nitride, an Aluminum oxide, a Zirconia, etc.) andthe like, or combinations thereof. The second end of the ultrasonicprobe 304 may comprise an ultrasonic probe tip 310. The ultrasonic probetip 310 may comprise niobium. Alternatively, the tip 310 may consistentessentially of, or consist of, niobium. Niobium may be alloyed with oneor more other metals, or niobium may be a layer that is plated or coatedonto a base layer of another material. For instance, the tip 310 maycomprise an inner layer and an outer layer, wherein the inner layer maycomprise a ceramic or a metal material (e.g., titanium) and the outerlayer may comprise niobium. In this embodiment, the thickness of theouter layer comprising niobium may be less than about 25 microns, orless than about 10 microns, or alternatively, within a range from about2 to about 8 microns. For example, the thickness of the outer layercomprising niobium may be in range from about 3 to about 6 microns.

The ultrasonic probe shaft 306 and the ultrasonic probe tip 310 may bejoined by a connector 308. The connector 308 may represent a means forattaching the shaft 306 and the tip 310. For example the shaft 306 andthe tip 310 may be bolted or soldered together. In one embodiment, theconnector 308 may represent that the shaft 306 contains recessedthreading and the tip 310 may be screwed into the shaft 306. It iscontemplated that the ultrasonic probe shaft 306 and the ultrasonicprobe tip 310 may comprise different materials. For instance, theultrasonic probe shaft 306 may be or may comprise titanium and/orniobium, while the ultrasonic probe tip 310 may be or may compriseniobium. Alternatively, the ultrasonic probe shaft 306 may be or maycomprise titanium and/or a ceramic (e.g., a Sialon, a Silicon carbide, aBoron carbide, a Boron nitride, a Silicon nitride, an Aluminum nitride,an Aluminum oxide, a Zirconia, etc.), while the ultrasonic probe tip 310may be or may comprise a ceramic (e.g., a Sialon, a Silicon carbide, aBoron carbide, a Boron nitride, a Silicon nitride, an Aluminum nitride,an Aluminum oxide, a Zirconia, etc.).

In other embodiments, the ultrasonic probe 304 may be a single piece,e.g., the ultrasonic probe shaft 306 and the ultrasonic probe tip 310are a unitary part having the same construction. In such instances, theultrasonic probe may comprise, for instance, niobium or an alloythereof, a ceramic (e.g., a Sialon, a Silicon carbide, a Boron carbide,a Boron nitride, a Silicon nitride, an Aluminum nitride, an Aluminumoxide, a Zirconia, etc.), or other suitable material.

Referring again to FIG. 3, the ultrasonic device 300 may comprise aninner tube 328, a center tube 324, an outer tube 320, and a protectiontube 340. These tubes or channels may surround at least a portion of theultrasonic probe 304 and generally may be constructed of any suitablemetal or ceramic material. It may be expected that the ultrasonic probetip 310 will be placed into the bath of molten metal; however, it iscontemplated that a portion of the protection tube 340 also may beimmersed in molten metal. Accordingly, the protection tube 340 may be ormay comprise titanium, niobium, a ceramic (e.g., a Sialon, a Siliconcarbide, a Boron carbide, a Boron nitride, a Silicon nitride, anAluminum nitride, an Aluminum oxide, a Zirconia, etc.), or a combinationof more than one of these materials. Contained within the tubes 328,324, 320, and 340 may be fluids 322, 326, and 342, as illustrated inFIG. 3. The fluid may be a liquid or a gas (e.g., argon), the purpose ofwhich may be to provide cooling to the ultrasonic device 300 and, inparticular, to the ultrasonic probe tip 310 and the protection tube 340.

The ultrasonic device 300 may comprise an end cap 344. The end cap maybridge the gap between the protection tube 340 and the probe tip 310 andmay reduce or prevent molten metal from entering the ultrasonic device300. Similar to the protection tube 340, the end cap 344 may be or maycomprise, for example, titanium, niobium, a ceramic (e.g., a Sialon, aSilicon carbide, a Boron carbide, a Boron nitride, a Silicon nitride, anAluminum nitride, an Aluminum oxide, a Zirconia, etc.), or a combinationof more than one of these materials.

The ultrasonic probe tip 310, the protection tube 340, or the end cap344, or all three, may comprise niobium. Niobium alone may be used,niobium may be alloyed with one or more other metals, or niobium may bea layer that is plated or coated onto a base layer of another material.For instance, the ultrasonic probe tip 310, the protection tube 340, orthe end cap 344, or all three, may comprise an inner layer and an outerlayer, wherein the inner layer may comprise a ceramic or a metalmaterial and the outer layer may comprise niobium. It may be expectedthat the presence of niobium on parts of the ultrasonic device mayimprove the life of the device, may provide low or no chemicalreactivity when in contact with molten metals, may provide strength atthe melting temperature of the molten metal, and may have the capabilityto propagate ultrasonic waves. In accordance with some embodiments ofthis invention, when the tip 310 of the ultrasonic device does notcomprise niobium, the tip may show erosion or degradation after onlyabout 15-30 minutes in a molten metal bath (e.g., of aluminum orcopper). In contrast, when the tip of the ultrasonic device comprisesniobium, the tip may show no or minimal erosion or degradation after atleast 1 hour or more, for instance, no erosion or degradation after atleast 2 hours, after at least 3 hours, after at least 4 hours, after atleast 5 hours, after at least 6 hours, after at least 12 hours, after atleast 24 hours, after at least 48 hours, or after at least 72 hours.

In another embodiment, the ultrasonic probe tip 310, the protection tube340, or the end cap 344, or all three, may comprise a ceramic, such as aSialon, a Silicon carbide, a Boron carbide, a Boron nitride, a Siliconnitride, an Aluminum nitride, an Aluminum oxide, and/or a Zirconia, andthe like. Further, the ultrasonic probe shaft 306 may comprise aceramic, or alternatively, titanium.

FIG. 4 illustrates another ultrasonic device 400 that may compriseniobium, a ceramic such as a Sialon, a Silicon carbide, a Boron carbide,a Boron nitride, a Silicon nitride, an Aluminum nitride, an Aluminumoxide, and/or a Zirconia, or other suitable material. The ultrasonicdevice 400 may include an ultrasonic transducer 460, a booster 450 forincreased output, and an ultrasonic probe assembly 402 attached to thetransducer 460. The booster 450 may permit increased output at boostlevels greater than about 1:1, for instance, from about 1.2:1 to about10:1, or from about 1.4:1 to about 5:1. A booster clamp assembly 451having a height H may be employed, where the height H may vary as neededto accommodate different length ultrasonic probes. The ultrasonic probeassembly 402 may comprise an elongated ultrasonic probe as depicted inFIG. 3 and an ultrasonic probe tip 410. The ultrasonic probe and tip maybe constructed of various materials, as previously discussed, including,but not limited to, stainless steel, titanium, niobium, ceramics, andthe like, or combinations thereof, inclusive of mixtures thereof, alloysthereof, and coatings thereof.

The ultrasonic device 400 may comprise a means for introducing a purginggas (e.g., into a molten metal bath) at a location near the ultrasonicdevice 400. It is contemplated that an external purging gas injectionsystem (not shown) may be positioned in the molten metal bath, and theinjection site may be near the ultrasonic device of FIG. 3 and/or FIG.4. Alternatively, the ultrasonic device may comprise a purging gasoutlet, such that the purging gas may be expelled near or at the tip ofthe ultrasonic device. For instance, the purging gas may be expelledthrough the end cap of the ultrasonic device and/or through the probe ofthe ultrasonic device. Referring again to FIG. 4, the ultrasonic devicemay comprise a purging gas inlet port 424 and injection chamber 425,connected to a purging gas delivery channel 413. The purging gas may bedelivered to, and expelled through, a purging gas delivery space 414located near or at the tip 410 of the ultrasonic device 400. It iscontemplated that the purging gas delivery space 414, or purging gasoutlet, may be within about 10 cm of the tip 410 of the ultrasonicdevice 400, such as, for example, within about 5 cm, within about 3 cm,within about 2 cm, within about 1.5 cm, within about 1 cm, or withinabout 0.5 cm, of the tip of the ultrasonic device.

Additionally, the ultrasonic device 400 may comprise an ultrasoniccooler system 429, which may be designed to keep the ultrasonic tipand/or the ultrasonic probe and/or the ultrasonic probe assembly at atemperature closer to room temperature (e.g., the temperature may be ina range from about 15° C. to about 75° C., or from about 20° C. to about35° C.), as opposed to the elevated temperatures of molten metalexperienced by the outer surface of the tip 410 of the ultrasonicdevice. It is contemplated that an ultrasonic cooler system may not berequired if the ultrasonic probe and assembly comprise niobium, aceramic such as a Sialon, a Silicon carbide, a Boron carbide, a Boronnitride, a Silicon nitride, an Aluminum nitride, an Aluminum oxide,and/or a Zirconia, or other suitable material. The ultrasonic coolersystem 429 of FIG. 4 may be similar to that system depicted in FIG. 3including, for instance, an inner tube 328, a center tube 324, an outertube 320, a protection tube 340, and fluids 322, 326, and 342, designedto provide cooling and/or temperature control to the ultrasonic device.The fluid may be a liquid or a gas, and it is contemplated that thefluid may be the same material as the purging gas.

FIG. 5 illustrates yet another ultrasonic device 500 that may compriseniobium, a ceramic such as a Sialon, a Silicon carbide, a Boron carbide,a Boron nitride, a Silicon nitride, an Aluminum nitride, an Aluminumoxide, and/or a Zirconia, or other suitable material. The ultrasonicdevice 500 may include an ultrasonic transducer 560, a booster 550 forincreased output, and an ultrasonic probe assembly 510 attached to thetransducer 560. The booster 550 may permit increased output at boostlevels greater than about 1:1, for instance, from about 1.2:1 to about10:1, or from about 1.4:1 to about 5:1. The ultrasonic probe 510 may bea single piece, or the ultrasonic probe 510 may comprise an ultrasonicprobe shaft and an optional (and replaceable) ultrasonic probe tip 511,similar to that depicted in FIG. 3. The ultrasonic probe and tip may beconstructed of various materials, as previously discussed, including,but not limited to, stainless steel, titanium, niobium, ceramics, andthe like, or combinations thereof, inclusive of mixtures thereof, alloysthereof, and coatings thereof.

The ultrasonic device 500 may comprise a means for introducing a purginggas (e.g., into a molten metal bath) at a location near the ultrasonicdevice 500 and/or near the ultrasonic probe tip 511. As above, it iscontemplated that an external purging gas injection system (not shown)may be positioned in the molten metal bath, and the injection site maybe near the ultrasonic device of FIG. 5. Alternatively, the ultrasonicdevice may comprise a purging gas outlet, such that the purging gas maybe expelled near or at the tip of the ultrasonic device. For instance,the purging gas may be expelled through the probe/tip of the ultrasonicdevice. Referring again to FIG. 5, the ultrasonic device may comprise apurging gas inlet port 522 in a chamber with the booster 550, an upperhousing 520, lower support housing 521, and a lower support housingcover 523. The upper housing 520 may be gas tight and/or leak proof. Thepurging gas inlet port 522 may be connected to a purging gas deliverychannel 524, which may be contained within the ultrasonic probe 510. Thepurging gas may be delivered to, and expelled through, a purging gasinjection point 525 (or purging gas outlet port) located at the tip 511of the ultrasonic device 500. Accordingly, in this embodiment, theultrasonic device 500 may comprise an ultrasonic probe 510 comprising apurging gas injection system with a purging gas injection point at thetip of the ultrasonic probe.

Optionally, the ultrasonic device 500 may comprise an ultrasonic coolersystem, such as described above relative to FIG. 3 and/or FIG. 4, butthis is not a requirement.

Another ultrasonic device is illustrated in FIG. 6. The ultrasonicdevice 600 may include an ultrasonic transducer 660, a booster 650 forincreased output, and an ultrasonic probe 610 attached to the transducer660 and booster 650. The booster 650 may be in communication with thetransducer 660, and may permit increased output at boost levels greaterthan about 1:1, for instance, from about 1.2:1 to about 10:1, or fromabout 1.4:1 to about 5:1. In some embodiments, the booster may be or maycomprise a metal, such as titanium. The ultrasonic probe 610 may be asingle piece, or the ultrasonic probe 610 may comprise an ultrasonicprobe shaft and an optional (and replaceable) ultrasonic probe tip,similar to that depicted in FIG. 3. The ultrasonic probe 610 is notlimited in shape and design to an elongated probe (e.g., generallycylindrical) with one end attached to the transducer 660 and/or booster650, and the other end comprising a tip of the probe. In one embodiment,the probe may be generally cylindrical, however, a middle portion of theprobe may be secured to the transducer/booster with a clamp or otherattachment mechanism, such that probe has two tips, neither of which isattached directly to the transducer/booster. Yet, in another embodiment,the probe may be another geometric shape, such as spherical, orcylindrical with a spherical portion at the tip, etc.

The ultrasonic probe 610 may be constructed of various materials, aspreviously discussed, including, but not limited to, stainless steel,titanium, niobium, ceramics, and the like, or combinations thereof,inclusive of mixtures thereof, alloys thereof, and coatings thereof. Incertain embodiments, the ultrasonic probe 610 may be or may comprise aceramic material. For instance, the ultrasonic probe may be or maycomprise a Sialon, a Silicon carbide, a Boron carbide, a Boron nitride,a Silicon nitride, an Aluminum nitride, an Aluminum oxide, a Zirconia,or a combination thereof; alternatively, a Sialon; alternatively, aSilicon carbide; alternatively, a Boron carbide; alternatively, a Boronnitride; alternatively, a Silicon nitride; alternatively, an Aluminumnitride; alternatively, an Aluminum oxide; or alternatively, a Zirconia.In some embodiments, the ultrasonic probe 610 may be a single piece,e.g., the probe is a unitary part, having the same construction orcomposition from the end attached to the transducer/booster to the probetip.

Typical Sialons that may be used in embodiments disclosed herein areceramic alloys containing the elements silicon (Si), aluminum (Al),oxygen (O) and nitrogen (N). Moreover, as would be recognized by one ofskill in the art, there are α-Sialon and β-Sialon grades. The ultrasonicprobe 610 may comprise a Sialon, and further, at least 20% (by weight)of which may be α-Sialon (or β-Sialon). While not wishing to be bound bytheory, Applicant believes that the use of at least 20% (by weight), or30% (by weight), or a weight percent in a range from about 20% to about50%, of a β-Sialon may provide a stronger and more durable ultrasonicprobe (e.g., less prone to breakage).

The ultrasonic device 600 may comprise a means for introducing a gas(e.g., a purging gas into a molten metal bath) at a location near theultrasonic device 600 and/or near the ultrasonic probe tip. As above, itis contemplated that an external purging gas injection system (notshown) may be positioned in the molten metal bath, and the injectionsite may be near the ultrasonic device of FIG. 6. Alternatively, theultrasonic device may comprise a gas delivery system, such that a gasmay be expelled near or at the tip of the ultrasonic device. Forinstance, the gas may be expelled through the probe/tip of theultrasonic device. Referring again to FIG. 6, the ultrasonic device 600may comprise a gas inlet port 622 in a chamber in the booster 650. Thegas inlet port 622 may be connected to a gas delivery channel 624, whichmay extend from the booster 650 to the tip of the ultrasonic probe 610.The gas inlet port 622 and part of the booster 650 may be containedwithin a gas tight and/or leak proof housing. The gas may be deliveredto, and expelled through, a gas injection point 625 (or gas outlet)located at the tip of the ultrasonic probe 610. Accordingly, in thisembodiment, the ultrasonic device 600 may comprise an ultrasonic probe610 comprising a gas delivery system with a gas injection point at thetip of the ultrasonic probe.

The gas delivery channel 624 is shown in FIG. 6 as having a larger flowpath in the booster 650 and a portion of the ultrasonic probe 610closest to the booster, and a smaller flow path at the gas injectionpoint 625, although this is not a requirement. For instance, the size ofthe gas delivery channel 624 may be substantially the same size (e.g.,within +/−10-20%) from the gas inlet port 622 to the gas injection point625 at the tip of the ultrasonic probe 610.

While not wishing to be bound by theory, Applicant believes that asmaller flow path (e.g., cross-sectional area) at the gas injectionpoint, relative to the cross-sectional area of the ultrasonic probe, mayresult in superior degassing due to the higher velocity of the gas as itexits the probe. In some embodiments, the ratio of the cross-sectionalarea of the ultrasonic probe to the cross-sectional area of the gasdelivery channel (i.e., at the gas injection point or gas outlet) may bein a range from about 30:1 to about 1000:1, from about 60:1 to about1000:1, or from about 60:1 to about 750:1. In other embodiments, theratio of the cross-sectional area of the ultrasonic probe to thecross-sectional area of the gas delivery channel (i.e., at the gasinjection point or gas outlet) may be in a range from about 60:1 toabout 700:1, from about 100:1 to about 700:1, or from about 200:1 toabout 1000:1. In these and other embodiments, the length to diameterratio (L/D) of the ultrasonic probe (e.g., a unitary elongated probe)may be in a range from about 5:1 to about 25:1, from about 5:1 to about12:1, from about 7:1 to about 22:1, from about 10:1 to about 20:1, orfrom about 11:1 to about 18:1.

In embodiments directed to ultrasonic probes containing a ceramicmaterial, such as a Sialon, it may be beneficial to employ an attachmentnut 603 as a means for securing the ultrasonic probe 610 to the booster650 and transducer 660. The attachment nut 603 may offer superiordurability and longevity as compared to shrink-fit ceramic attachments.The attachment nut 603 may be constructed of various materials, such as,for instance, titanium, stainless steel, etc., and may contain finepitch (internal) treads for robust securement, alleviating the need tohave a threaded ceramic probe which is more prone to breakage. Moreover,the booster 650 may have external threads, onto which the attachment nut603 (and, therefore, the probe 610) may be robustly secured. Generally,it also may be beneficial to keep the size and/or weight of theattachment nut as low as is mechanically feasible, such that ultrasonicvibrational properties of the probe are not adversely affected.

In certain embodiments, the probe 610 may have a large radius ofcurvature 615 at the attachment side of the probe. While not wishing tobe bound by theory, Applicant believes that a smaller radius ofcurvature at the attachment side of the probe (e.g., proximate to theattachment nut) may lead to increased breakage of the probe,particularly at higher ultrasonic powers and/or amplitudes that mayrequired for increased cavitation and superior dissolved gas removal ina degassing process. In particular embodiments contemplated herein, theradius of curvature 615 may be at least about ½″, at least about ⅝″, atleast about ¾″, at least about 1″, and so forth. Such radiuses ofcurvature may be desirable regardless of the actual size of the probe(e.g., various probe diameters).

Optionally, the ultrasonic device 600 may comprise an ultrasonic coolersystem, such as described above relative to FIG. 3 and/or FIG. 4, butthis is not a requirement. Referring again to FIG. 6, the ultrasonicdevice 600, alternatively, may optionally comprise a thermal protectionhousing 640. This housing generally may be constructed of any suitablemetal and/or ceramic material. It may be expected that the ultrasonicprobe 610 will be placed into the bath of molten metal; therefore, thethermal protection housing may be used to shield a portion of thebooster 650, the attachment nut 603, and a portion of the ultrasonicprobe 610 from excessive heat. If desired, a cooling medium may becirculated within and/or around the thermal protection housing 640. Thecooling medium may be a liquid (e.g., water) or a gas (e.g., argon,nitrogen, air, etc.).

The ultrasonic devices disclosed herein, including those illustrated inFIGS. 3-6, may be operated at a range of powers and frequencies. Forultrasonic devices with probe diameters of about 1″ or less, theoperating power often may be in a range from about 60 to about 275watts. As an example, operating power ranges of about 60 to about 120watts for ¾″ probe diameters, and operating power ranges of about 120 toabout 250 watts for 1″ probe diameters, may be employed. While not beinglimited to any particular frequency, the ultrasonic devices may beoperated at, and the ultrasonic degassing methods may be conducted at, afrequency that typically may be in a range from about 10 to about 50kHz, from about 15 to about 40 kHz, or at about 20 kHz.

Referring now to FIGS. 7A-7B, which illustrate an ultrasonic probe 710that may be used in any of the ultrasonic devices of FIGS. 3-6. Asillustrated, the ultrasonic probe 710 is shown as a single piece(unitary part), but may comprise an ultrasonic probe shaft and anoptional (and replaceable) ultrasonic probe tip, as describedhereinabove for FIG. 3, in certain embodiments. Additionally, theultrasonic probe 710 is shown as an elongated probe (e.g., generallycylindrical), but is not limited to this geometric shape.

The ultrasonic probe 710 may be constructed of various materials, asdiscussed herein, including, but not limited to, stainless steel,titanium, niobium, ceramics, and the like, or combinations thereof,inclusive of mixtures thereof, alloys thereof, and coatings thereof. Incertain embodiments, the ultrasonic probe 710 may be or may comprise aceramic material. For instance, the ultrasonic probe 710 may be or maycomprise a Sialon, a Silicon carbide, a Boron carbide, a Boron nitride,a Silicon nitride, an Aluminum nitride, an Aluminum oxide, a Zirconia,or a combination thereof; alternatively, a Sialon (e.g., any Sialondisclosed herein); alternatively, a Silicon carbide; alternatively, aBoron carbide; alternatively, a Boron nitride; alternatively, a Siliconnitride; alternatively, an Aluminum nitride; alternatively, an Aluminumoxide; or alternatively, a Zirconia.

The ultrasonic probe 710 may comprise a gas channel 724 in the center ofthe probe and extending the full length of the probe, with a gas outlet725 at the tip of the probe. A purging gas may be delivered through thegas channel 724 and expelled at the gas outlet 725 at the tip of theultrasonic probe 710. In some embodiments, the ratio of thecross-sectional area of the ultrasonic probe 710 to the cross-sectionalarea of the gas channel 724 (e.g., anywhere within the length of theprobe, or at the gas outlet 725) may be in a range from about 30:1 toabout 1000:1, from about 60:1 to about 1000:1, or from about 60:1 toabout 750:1. In other embodiments, the ratio of the cross-sectional areaof the ultrasonic probe 710 to the cross-sectional area of the gaschannel 724 may be in a range from about 60:1 to about 700:1, from about100:1 to about 700:1, from about 50:1 to about 500:1, or from about200:1 to about 1000:1. In these and other embodiments, the length todiameter ratio (L/D) of the ultrasonic probe 710 may be in a range fromabout 5:1 to about 25:1, from about 5:1 to about 15:1, from about 5:1 toabout 12:1, from about 7:1 to about 22:1, from about 7:1 to about 14:1,from about 10:1 to about 20:1, or from about 11:1 to about 18:1.

The ultrasonic probe 710 may be secured to an ultrasonic device usingany suitable method known to those of skill in art, for example, usingan attachment nut as described herein. In certain embodiments, the probe710 may have a large radius of curvature 715 at the attachment side ofthe probe, which may reduce probe breakage and increase the useful lifeof the probe. In particular embodiments contemplated herein, the radiusof curvature 715 may be at least about ⅛″, at least about ¼″, at leastabout ½″, at least about ⅝″, at least about ¾″, at least about 1″, andso forth (e.g., the radius of curvature 715 may be equal to about ¼″).Such radiuses of curvature may be desirable regardless of the actualsize of the probe (e.g., various probe diameters).

FIGS. 1A-1B illustrate an ultrasonic probe 110 that may be used in anyof the ultrasonic devices of FIGS. 3-6. As illustrated, the ultrasonicprobe 110 is shown as a single piece (unitary part), but may comprise anultrasonic probe shaft and an optional (and replaceable) ultrasonicprobe tip, as described hereinabove for FIG. 3, in certain embodiments.Additionally, the ultrasonic probe 110 is shown as an elongated probe(e.g., generally cylindrical), but is not limited to this geometricshape.

The ultrasonic probe 110 may be constructed of various materials, asdiscussed herein, including, but not limited to, stainless steel,titanium, niobium, ceramics, and the like, or combinations thereof,inclusive of mixtures thereof, alloys thereof, and coatings thereof. Incertain embodiments, the ultrasonic probe 110 may be or may comprise aceramic material. For instance, the ultrasonic probe 110 may be or maycomprise a Sialon, a Silicon carbide, a Boron carbide, a Boron nitride,a Silicon nitride, an Aluminum nitride, an Aluminum oxide, a Zirconia,or a combination thereof; alternatively, a Sialon (e.g., any Sialondisclosed herein); alternatively, a Silicon carbide; alternatively, aBoron carbide; alternatively, a Boron nitride; alternatively, a Siliconnitride; alternatively, an Aluminum nitride; alternatively, an Aluminumoxide; or alternatively, a Zirconia.

The ultrasonic probe 110 may comprise a plurality of gas channels 124extending the full length of the probe, with associated gas outlets 125at the tip of the probe. In FIGS. 1A-1B, a probe 110 with three gaschannels 124 is shown; however, the probe may have two gas channels, orfour or more gas channels, in other embodiments. Moreover, the gaschannels may be positioned anywhere within the interior of the probe.FIGS. 1A-1B show the three gas channels 124 positioned about halfwayfrom the center to the exterior surface of the probe, and arranged about120° apart. A purging gas may be delivered through the gas channels 124and expelled at the gas outlets 125 at the tip of the ultrasonic probe110. In some embodiments, the ratio of the cross-sectional area of theultrasonic probe 110 to the total cross-sectional area of the three gaschannels 124 (e.g., anywhere within the length of the probe, or at thegas outlets 125) may be in a range from about 30:1 to about 1000:1, fromabout 60:1 to about 1000:1, or from about 60:1 to about 750:1. In otherembodiments, the ratio of the cross-sectional area of the ultrasonicprobe 110 to the total cross-sectional area of the three gas channels124 may be in a range from about 20:1 to about 250:1, from about 20:1 toabout 175:1, from about 30:1 to about 200:1, from about 30:1 to about175:1, from about 60:1 to about 700:1, from about 100:1 to about 700:1,from about 50:1 to about 500:1, or from about 200:1 to about 1000:1. Inthese and other embodiments, the length to diameter ratio (L/D) of theultrasonic probe 110 may be in a range from about 5:1 to about 25:1,from about 5:1 to about 15:1, from about 5:1 to about 12:1, from about7:1 to about 22:1, from about 7:1 to about 14:1, from about 10:1 toabout 20:1, or from about 11:1 to about 18:1.

The ultrasonic probe 110 may be secured to an ultrasonic device usingany suitable method known to those of skill in art, for example, usingan attachment nut as described herein. In certain embodiments, the probe110 may have a large radius of curvature 115 at the attachment side ofthe probe, which may reduce probe breakage and increase the useful lifeof the probe. In particular embodiments contemplated herein, the radiusof curvature 115 may be at least about ⅛″, at least about ¼″, at leastabout ½″, at least about ⅝″, at least about ¾″, at least about 1″, andso forth (e.g., the radius of curvature 115 may be equal to about ¼″).Such radiuses of curvature may be desirable regardless of the actualsize of the probe (e.g., various probe diameters).

Illustrated in FIG. 1C is an ultrasonic device 100 with an ultrasonictransducer 160, a booster 150 for increased output, and an ultrasonicprobe 110 (described hereinabove) attached to the booster 150 andtransducer 160. The booster 150 may be in communication with thetransducer 160, and may permit increased output at boost levels greaterthan about 1:1, for instance, from about 1.2:1 to about 10:1, or fromabout 1.4:1 to about 5:1. In some embodiments, the booster may be or maycomprise a metal, such as titanium. The ultrasonic device 100 maycomprise a gas inlet (two gas inlets 122 are shown in FIG. 1C) thatfeeds a gas flow line that terminates at the end of booster. The probe110 may be secured to the booster 150 with an attachment nut 103. Asingle gas delivery channel 124 is shown is FIG. 1C, with a gas outlet125 at the tip of the probe. Two other gas delivery channels are presentin the probe, but are not shown in the cross-sectional view of FIG. 1C.

FIG. 1D is a close-up view of portions of the ultrasonic device andprobe of FIGS. 1A-1C, illustrating the interface between the booster 150and the probe 110, secured with the attachment nut 103. A single gasinlet (or gas flow line) may be used for each gas delivery channel 124in the probe 110, or alternatively, a single gas inlet may be used, andthe flow may be split in the booster to form three flow paths whichconnect to the respective gas delivery channels in the probe. Anotheroption is demonstrated in FIG. 1D, where a gas inlet 122 (or gas flowline) terminates in a recessed gas chamber 118 at the end of booster150, the purging gas disposed between (and bounded by) the booster 150and the probe 110, and the recessed gas chamber 118 may be gas tight orleak proof. The recessed gas chamber 118 may be configured to direct thepurging gas flow from the booster 150 to the three gas delivery channels124 in the probe 110. The recessed gas chamber 118 can be of anysuitable geometry, but is illustrated as a parabolic shape (e.g., like acontact lens) in FIG. 1D.

FIGS. 2A-2B illustrate an ultrasonic probe 210 that may be used in anyof the ultrasonic devices of FIGS. 3-6. As illustrated, the ultrasonicprobe 210 is shown as a single piece (unitary part), but may comprise anultrasonic probe shaft and an optional (and replaceable) ultrasonicprobe tip, as described hereinabove for FIG. 3, in certain embodiments.Additionally, the ultrasonic probe 210 is shown as an elongated probe(e.g., generally cylindrical), but is not limited to this geometricshape.

The ultrasonic probe 210 may be constructed of various materials, asdiscussed herein, including, but not limited to, stainless steel,titanium, niobium, ceramics, and the like, or combinations thereof,inclusive of mixtures thereof, alloys thereof, and coatings thereof. Incertain embodiments, the ultrasonic probe 210 may be or may comprise aceramic material. For instance, the ultrasonic probe 210 may be or maycomprise a Sialon, a Silicon carbide, a Boron carbide, a Boron nitride,a Silicon nitride, an Aluminum nitride, an Aluminum oxide, a Zirconia,or a combination thereof; alternatively, a Sialon (e.g., any Sialondisclosed herein); alternatively, a Silicon carbide; alternatively, aBoron carbide; alternatively, a Boron nitride; alternatively, a Siliconnitride; alternatively, an Aluminum nitride; alternatively, an Aluminumoxide; or alternatively, a Zirconia.

The ultrasonic probe 210 may comprise a gas channel 224 in the center ofthe probe and extending the full length of the probe, with one gasoutlet 225 at the tip of the probe. The probe 210 also may contain aplurality of recessed areas 235 near the tip of the probe. In FIGS.2A-2B, a probe 210 with three recessed areas 235 is shown, however, theprobe may have only one or two recessed areas, or four or more recessedareas, in other embodiments. Moreover, the recessed areas are notlimited to any particular depth and/or width. FIGS. 2A-2B show recessedareas 235 having a diameter of about 75-85% of the diameter of theultrasonic probe 210, and a total length of the three recessed areassuch that the ratio of length of the probe 210 to the total length ofthe three recessed areas 235 may be in a range from about 10:1 to about100:1, or from about 15:1 to about 80:1.

The ultrasonic probe 210 also contains four gas outlets 225 in therecessed area 235 closest to the tip of the probe. One of these gasoutlets is shown in FIG. 2A; the other three are located 90° around thecircumference of the probe. A purging gas may be delivered through thegas channel 224 and expelled at the gas outlets 225 in the recessed areaand at the tip of the ultrasonic probe 210. In some embodiments, theratio of the cross-sectional area of the ultrasonic probe 210 to thetotal cross-sectional area of the gas channel 224 at the gas outlets 225(i.e., at the five gas outlets) may be in a range from about 30:1 toabout 1000:1, from about 60:1 to about 1000:1, or from about 60:1 toabout 750:1. In other embodiments, the ratio of the cross-sectional areaof the ultrasonic probe 210 to the total cross-sectional area of the gaschannels at the gas outlets may be in a range from about 20:1 to about250:1, from about 20:1 to about 175:1, from about 30:1 to about 200:1,from about 30:1 to about 175:1, from about 60:1 to about 700:1, fromabout 100:1 to about 700:1, from about 50:1 to about 500:1, or fromabout 200:1 to about 1000:1. In these and other embodiments, the lengthto diameter ratio (L/D) of the ultrasonic probe 210 may be in a rangefrom about 5:1 to about 25:1, from about 5:1 to about 15:1, from about5:1 to about 12:1, from about 7:1 to about 22:1, from about 7:1 to about14:1, from about 10:1 to about 20:1, or from about 11:1 to about 18:1.

The ultrasonic probe 210 may be secured to an ultrasonic device usingany suitable method known to those of skill in art, for example, usingan attachment nut as described herein. In certain embodiments, the probe210 may have a large radius of curvature 215 at the attachment side ofthe probe, which may reduce probe breakage and increase the useful lifeof the probe. In particular embodiments contemplated herein, the radiusof curvature 215 may be at least about ⅛″, at least about ¼″, at leastabout ½″, at least about ⅝″, at least about ¾″, at least about 1″, andso forth (e.g., the radius of curvature 215 may be equal to about ¼″).Such radiuses of curvature may be desirable regardless of the actualsize of the probe (e.g., various probe diameters).

While certain embodiments of the invention have been described, otherembodiments may exist. Further, any disclosed methods' stages may bemodified in any manner, including by reordering stages and/or insertingor deleting stages, without departing from the invention. While thespecification includes examples, the invention's scope is indicated bythe following claims. Furthermore, while the specification has beendescribed in language specific to structural features and/ormethodological acts, the claims are not limited to the features or actsdescribed above. Rather, the specific features and acts described aboveare disclosed as illustrative embodiments of the invention.

EXAMPLES Examples 1-4

In Examples 1-4, a series of tests were conducted to determine therelative speed at which dissolved hydrogen in a molten bath of aluminumcan be degassed in accordance with the disclosed methods. First, a smallamount of aluminum was melted in a metal bath, and then maintained, at atemperature of about 1350° F. (732° C.). An Alspek unit was used todetermine a baseline reading of hydrogen content, in units of mL/100 g.The Alspek unit uses the principle of partial pressures in anelectrolytic half cell to determine the amount of dissolved hydrogen inmolten aluminum. The tip of an ultrasonic device was placed into thealuminum bath, and the purging gas argon was added to the molten metalbath at a rate of about 1 standard liter per minute (L/min). ForExamples 1-4, the ultrasonic device was operated with a 3:1 booster andat 20,000 Hz, although up to and including 40,000 Hz, or more, could beused. For Example 1, a baseline ultrasonic vibration amplitude was used,and a baseline power level for the ultrasonic power supply (watts); forExample 2, the ultrasonic vibration amplitude was 2 times the baseline,and the power level of the ultrasonic power supply was 1.9 times thebaseline; and for Example 3, the ultrasonic vibration amplitude was 3times the baseline, and the power level of the ultrasonic power supplywas 3.6 times the baseline. For Example 4, the ultrasonic device was notused, only addition of the argon purging gas. The level of hydrogen wasmonitored over time using the Alspek unit, and recorded. Between eachexperiment, hydrogen was added into the aluminum bath, and the baselinebefore the addition of the argon gas was determined.

An ultrasonic device similar to that illustrated in FIG. 5 was used inExamples 1-3. The ultrasonic device did not have a cooling assembly, andthe purging gas was injected thru the tip of the ultrasonic probe. Theultrasonic probe was 1″ (2.5 cm) in diameter, and both the probe and tip(as a single part) were constructed of a niobium alloy containinghafnium and titanium.

FIG. 8 illustrates a plot of hydrogen concentration in mL of hydrogenper 100 g of the aluminum alloy as a function of time after the additionof the argon purging gas (and the activation of the ultrasonic device,if used). FIG. 8 demonstrates the each of Examples 1-3 degassed hydrogenfrom aluminum significantly faster (using a purging gas and anultrasonic device) than that of Example 4, which only used a purginggas, but no ultrasonic device. Examples 2-3 performed slightly betterthan Example 1, which used a lower ultrasonic vibration amplitude and alower baseline power level for the ultrasonic power supply.

Examples 5-6

Examples 5-6 were large scale trials to determine the effectiveness ofusing a purging gas and an ultrasonic device to remove hydrogen andlithium/sodium impurities in a continuous casting experiment usingaluminum alloy 5154 (containing magnesium). The temperature of the metalbath was maintained at a temperature of about 1350° F. (732° C.).

Sodium and lithium concentrations in weight percent were determinedusing a spectrometer, and hydrogen concentrations were determined usingan Alscan hydrogen analyzer for molten aluminum. Example 5 was a controlexperiment, and the prevailing sodium and lithium concentrations in themolten aluminum alloy of Example 5 were 0.00083% (8.3 ppm) and 0.00036%(3.6 ppm), respectively. The hydrogen concentration in Example 5 was0.41 mL/100 g.

The ultrasonic device of Examples 1-4 was used in Example 6 and operatedat 20,000 Hz. In conjunction with the operation of the ultrasonicdevice, in Example 6, argon gas was added to the molten metal bath at avolumetric flow rate of about 80-85 mL/hr per kg/hr of molten metaloutput (i.e., 80-85 mL purging gas/kg molten metal). After the use ofthe ultrasonic device and the argon purging gas, the sodiumconcentration in the molten aluminum alloy was below the minimumdetection limit of 0.0001% (1 ppm by weight), and the lithiumconcentration in the molten aluminum alloy was 0.0003% (3 ppm byweight). The hydrogen concentration in Example 6 was 0.35 mL/100 g, areduction of about 15%.

Example 7

In Example 7, a test was conducted to determine the useful life orlongevity of an ultrasonic device with a unitary Sialon probe, similarto that illustrated in FIG. 6, operated in a launder containing moltenaluminum at approximately 1300° F. (700° C.).

The ultrasonic device and probe were operated continuously, except for a3-hour maintenance shutdown unrelated to the ultrasonic device. Theelongated probe was ¾″ in diameter, was made from Sialon, and wasoperated at about 20 kHz (19.97 kHz). Power levels were between 60 and90 watts. Using a digital gauge, the length of the probe was measuredbefore and after use. The probe tip was submerged for about 50 hours inthe launder containing the molten aluminum while the ultrasonic devicewas operated at about 20 KHz. No purging gas was used during thisexperiment, as it was deemed to be unnecessary for the purpose of thistest. After the 50-hour run time, the erosion of the probe was measuredto be 0.0182″. This converts to an erosion rate of 3.64×10⁻⁴ in/hour.Generally, an ultrasonic probe can withstand up to about ¼″ of erosionbefore it is deemed to be unfit for use. This leads to a theoreticallifetime of over 686 hours, or over 28 days, of continuous operation forthe ceramic probe of Example 7.

This probe lifetime is far superior to that of other metallic andceramic ultrasonic probes not designed, configured, or constructed asdescribed herein.

Examples 8-11

Examples 8-11 were performed in a manner similar to Examples 5-6. Table1 summarizes the results of the degassing experiments using Sialonprobes having the design of FIGS. 7A-7B (Example 8), the design of FIGS.2A-2B (Example 9), and the design of FIGS. 1A-1D (Example 10 and Example11). Table 1 also lists the flow rate of N₂, the power of the ultrasonicdevice, and the reduction in H₂ content of the metal in the molten metalbath. The results in Table 1 indicate that each of the probe designs wassuccessful in significantly reducing the amount of H₂ gas in the moltenmetal bath, with Examples 9-11 and their respective probe designsproviding a greater reduction in H₂ content. While not wishing to bebound by theory, the design of FIGS. 2A-2B (Example 9) may provideimproved cavitation efficiency due to the recessed regions. As to thedesign of FIGS. 1A-1D (Example 10 and Example 11), and not wishing to bebound by theory, the multiple gas channel design may provide an increasein overall gas flow (15-20 L/min in 3 channels vs. 5 L/min in onechannel), whereas using an equivalent 15-20 L/min gas velocity exitingthe probe in a single channel may be too high for certain molten metalapplications, effectively “blowing” metal away from the probe.

TABLE 1 Summary of Examples 8-11. Probe Example Diameter Probe Gas FlowPower Reduction Number (inches) Design (L/min) (Watts) In H₂ (%) 8 0.75FIGS. 5 80 42.8% 7A-7B 9 0.75 FIGS. 7 125 76.0% 2A-2B 10 0.875 FIGS. 15100 57.3% 1A-1D 11 0.875 FIGS. 20 100 74.5% 1A-1D

Examples 12-24

Examples 12-24 were performed in a manner similar to Examples 5-6. Table2 summarizes the results of the degassing experiments using Sialonprobes having the design of FIGS. 7A-7B (Examples 12-19) and the designof FIGS. 1A-1D (Examples 20-24). Table 2 also lists the flow rate of N₂,the power of the ultrasonic device, and the sodium (Na) content beforeand after degassing the metal in the molten metal bath. The results inTable 2 indicate that each of the probe designs was successful insignificantly reducing the impurity level of sodium. However, andunexpectedly, with Examples 20-24 and the respective probe design ofFIGS. 1A-1D, the sodium was removed to undetectable levels (shown aszero in Table 2, and less than 1 ppm by weight). While not wishing to bebound by theory, the improved design of FIGS. 1A-1D (Examples 20-24) mayprovide an increase in cavitation bubbles to collect and remove thesodium impurity, but without decreasing the ultrasonic vibrationefficiency and the cavitation efficiency.

TABLE 2 Summary of Examples 12-24. Sodium Sodium Probe Example BeforeAfter Diameter Probe Gas Flow Power Number (ppm) (ppm) (inches) Design(L/min) (Watts) 12 7 6 0.75 FIGS. 5 80 13 5 3 7A-7B 14 2 2 15 1 1 16 4 217 8 3 18 7 2 19 4 2 20 3 0 0.875 FIGS. 20 100 21 5 0 1A-1D 22 3 0 23 60 24 3 0

Examples 25-27

Examples 25-27 were performed in a manner similar to Examples 20-24,using a 0.875-inch diameter Sialon probe having the design of FIGS.1A-1D, and operated at 100 watts and an argon gas flow rate of 20 L/min.The surprising ability of the ultrasonic device with the probe design ofFIGS. 1A-1D to significantly reduce the inclusion concentration inmolten metal products was evaluated using three different metal alloys(5052, 6201, and 4047).

The amount of inclusions (mm²/kg) before and the amount of inclusionsafter ultrasonic degassing were determined by drawing respective samplesof the molten metal through a small filter under vacuum. The amount ofmetal drawn through the filter was weighed and discarded. The metal inthe filter was allowed to solidify. The filter was then cut from theremaining sample and sent to an ABB laboratory for PoDFA metallurgicalanalysis to determine the amount of inclusions.

Table 3 summarizes the % reduction in the total inclusions (or inclusionconcentration) as a result of the ultrasonic degassing process.Unexpectedly, the ultrasonic degassing experiments of Examples 25-27were able to remove at least 55% of the inclusions, and in Example 25,over 98% of the inclusions were removed.

TABLE 3 Summary of Examples 25-27. Example Reduction In Total NumberAlloy Inclusions (%) 25 5052 98.4% 26 6201 80.2% 27 4047 55.6%

I claim:
 1. An ultrasonic device comprising: an ultrasonic transducer;an ultrasonic probe attached to the transducer, the probe comprising atip and two or more gas delivery channels extending through the probe;and a gas delivery system, the gas delivery system comprising: a gasinlet, gas flow paths through the gas delivery channels, and gas outletsat or near the tip of the probe.
 2. The ultrasonic device of claim 1,wherein the probe comprises stainless steel, titanium, niobium, aceramic, or a combination thereof.
 3. The ultrasonic device of claim 1,wherein the probe comprises a Sialon, a Silicon carbide, a Boroncarbide, a Boron nitride, a Silicon nitride, an Aluminum nitride, anAluminum oxide, a Zirconia, or a combination thereof.
 4. The ultrasonicdevice of claim 1, wherein: the probe comprises a Sialon; the probecomprises from three to five gas delivery channels; and the gas outletsare at the tip of the probe.
 5. The ultrasonic device of claim 1,wherein the probe is a generally cylindrical elongated probe, and alength to diameter ratio of the elongated probe is in a range from about5:1 to about 25:1.
 6. The ultrasonic device of claim 1, wherein theprobe is a generally cylindrical elongated probe, and a ratio of thecross-sectional area of the tip of the elongated probe to thecross-sectional area of the gas delivery channels is in a range fromabout 30:1 to about 1000:1.
 7. The ultrasonic device of claim 1, whereinthe ultrasonic device further comprises a booster between the transducerand the probe, and the gas inlet is in the booster.
 8. The ultrasonicdevice of claim 7, wherein a recessed gas chamber at an end of thebooster connects to the gas inlet, the recessed gas chamber configuredto direct gas flow to the gas delivery channels.
 9. The ultrasonicdevice of claim 1, wherein the ultrasonic device comprises from two toeight ultrasonic probes.
 10. A method for reducing an amount of adissolved gas and/or an impurity in a molten metal bath, the methodcomprising: (a) operating the ultrasonic device of claim 1 in the moltenmetal bath; and (b) introducing a purging gas into the gas deliverysystem, through the gas delivery channels, and into the molten metalbath at a rate for each ultrasonic probe in a range from about 0.1 toabout 150 L/min.
 11. The method of claim 10, wherein: the dissolved gascomprises oxygen, hydrogen, SO₂, or a combination thereof; the impuritycomprises an alkali metal; the molten metal bath comprises aluminum,copper, zinc, steel, magnesium, or a combination thereof; the purginggas comprises nitrogen, helium, neon, argon, krypton, xenon, SF₆,chlorine, or a combination thereof; or any combination thereof.
 12. Themethod of claim 10, wherein: the purging gas is introduced into themolten metal bath at a rate for each ultrasonic probe in a range fromabout 1 to about 50 L/min; the dissolved gas comprises hydrogen; themolten metal bath comprises aluminum, copper, or a combination thereof;the purging gas comprises argon, nitrogen, or a combination thereof; orany combination thereof.
 13. The method of claim 10, wherein: theimpurity comprises sodium, and an amount of sodium in the molten metalbath is reduced to less than 1 ppm; and/or an amount of totalinclusions, in mm²/kg, in the molten metal bath is reduced by at leastabout 50%.
 14. The method of claim 10, wherein the method comprisesoperating from two to sixteen ultrasonic devices in the molten metalbath.
 15. An ultrasonic device comprising: an ultrasonic transducer; anultrasonic probe attached to the transducer, the probe comprising a tip,a gas delivery channel extending through the probe, and a recessedregion near the tip of the probe; and a gas delivery system, the gasdelivery system comprising: a gas inlet, a gas flow path through the gasdelivery channel, and a gas outlet at or near the tip of the probe;wherein the probe is a generally cylindrical elongated probe, and aratio of a total length of the recessed regions to a length of theelongated probe is in a range from about 10:1 to about 100:1.
 16. Theultrasonic device of claim 15, wherein the probe comprises stainlesssteel, titanium, niobium, a ceramic, or a combination thereof.
 17. Theultrasonic device of claim 15, further comprising a gas outlet in arecessed region.
 18. The ultrasonic device of claim 15, wherein theprobe comprises a Sialon; the probe comprises from two to five recessedregions; and at least one gas outlet is at the tip of the probe.
 19. Theultrasonic device of claim 15, wherein: the probe is a generallycylindrical elongated probe, and a length to diameter ratio of theelongated probe is in a range from about 5:1 to about 25:1; and a ratioof the cross-sectional area of the tip of the elongated probe to thecross-sectional area of the gas delivery channel is in a range fromabout 30:1 to about 1000:1.
 20. The ultrasonic device of claim 15,wherein the ultrasonic device further comprises a booster between thetransducer and the probe, and the gas inlet is in the booster.
 21. Amethod for reducing an amount of a dissolved gas and/or an impurity in amolten metal bath, the method comprising: (a) operating the ultrasonicdevice of claim 15 in the molten metal bath; and (b) introducing apurging gas into the gas delivery system, through the gas deliverychannel, and into the molten metal bath at a rate for each ultrasonicprobe in a range from about 0.1 to about 150 L/min.
 22. The method ofclaim 21, wherein: the purging gas is introduced into the molten metalbath at a rate for each ultrasonic probe in a range from about 1 toabout 50 L/min; the dissolved gas comprises oxygen, hydrogen, sulfurdioxide, or a combination thereof; the impurity comprises an alkalimetal; the molten metal bath comprises aluminum, copper, zinc, steel,magnesium, or a combination thereof; the purging gas comprises nitrogen,helium, neon, argon, krypton, xenon, SF₆, chlorine, or a combinationthereof; or any combination thereof.
 23. An ultrasonic devicecomprising: an ultrasonic transducer; an ultrasonic probe attached tothe transducer, the probe comprising a tip, a gas delivery channelextending through the probe, and a recessed region near the tip of theprobe; and a gas delivery system, the gas delivery system comprising: agas inlet, a gas flow path through the gas delivery channel, and a gasoutlet at or near the tip of the probe; wherein a diameter of therecessed region is from about 75 to about 85% of the diameter of theprobe.